title: Selection for vancomycin resistance in clinical isolates of Staphylococcus haemolyticus.
abstract: Killing curves were used to characterize Staphylococcus haemolyticus isolates previously reported to contain subpopulations showing increased resistance to vancomycin. Results suggested that vancomycin and teicoplanin were ineffective at a concentration of 8 micrograms/ml and growth was seen between 24 and 48 h. Conversely, the lipopeptide antibiotic daptomycin at the same concentration rapidly killed tested strains by 6 h. Various staphylococcal strains were examined to determine if vancomycin resistance could be selected in all strains of staphylococci, was specie(s) restricted, or was unique to this patient's clinical isolates. About 1 x 10(8) colony-forming units were added to melted brain-heart infusion agar plates containing 12 micrograms/ml of vancomycin. Plates were examined after 48 h for presence of resistant clones. Results indicated that selection for vancomycin resistance was restricted to S. haemolyticus strains. Further, all S. haemolyticus isolates that displayed a double zone of growth around imipenem agar diffusion discs (Impdz) contained stably resistant subpopulations. Vancomycin resistance could not be selected in imipenem-sensitive derivative clones. Impdz isolates that were recovered from geographically distinct locations displayed nearly identical SDS-PAGE protein profiles. It appears that a characteristic susceptibility pattern displayed by clinical isolates of S. haemolyticus may provide a marker for those strains that contain subpopulations having increased resistance to vancomycin.
authors.affiliation: Department of Medicine, Veterans Administration Medical Center, Albany, New York.
authors.forename: R S
authors.initials: RS
authors.lastname: Schwalbe
authors.forename: W J
authors.initials: WJ
authors.lastname: Ritz
authors.forename: P R
authors.initials: PR
authors.lastname: Verma
authors.forename: E A
authors.initials: EA
authors.lastname: Barranco
authors.forename: P H
authors.initials: PH
authors.lastname: Gilligan
mesh_terms: D001426:Bacterial Proteins / Q000032:analysis; D003030:Coagulase / Q000378:metabolism; D004352:Drug Resistance, Microbial; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D015378:Imipenem / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D013045:Species Specificity; D013210:Staphylococcus / Q000032:analysis / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification; D013997:Time Factors; D014640:Vancomycin / Q000494:pharmacology*
chemical_list: D001426:Bacterial Proteins; D003030:Coagulase; D014640:Vancomycin; D015378:Imipenem